This invention relates to a process for producing a flyback transformer.
Flyback transformers can be divided into two types, one of which is a flat winding type wherein layer insulation is carried out by using a polyester film and the other of which is a divided winding type wherein insulation is carried out by a platic bobbin having a plurality of dividing walls. The flyback transformer is further equipped with various parts such as one or more diodes, resistors for controlling output properties, capacitors, and the like and insulation treated to give a finished product.
Since a high voltage is applied to individual constituting parts of the flyback transformer, there often bring about delamination between parts and an insulating material and cracks in casted material due to the delamination, and once cracks are produced, there brings about corona discharge, which causes dielectric breakdown of the flyback transformer.
As the casting materials for flyback transformers, there have been used silicone resins, epoxy resins, and the like. Silicone resins can be cured fast and are excellent in flexiblity and electrical properties but are poor in adhesiveness with the parts as well as hygroscopic properties (moisture resistance) and are very expensive, which limit applicable kinds of devices. On the other hand, epoxy resins have advantages in excellent adhesiveness and moisture resistance, but are poor in temperature-dependency of electrical properties and have a long curing time. Improvement of these defects has long been desired.
As to unsaturated polyester resins, conventional ones have advantages in a short curing time and a long pot life, but have large curing shrinkage which causes delamination from parts and cases and produces cracks which bring about corona discharge, these being fatal defects for practically producing flyback transformers from unsaturated polyester resins.